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A detailed review of participants in FAPAS Series I Round 26 and Series X Round 16 was conducted, with the co-operation of the FAPAS Secretariat, in order to obtain details of the methods used for extraction and quantification of chloride. These data were analysed to find patterns or relationships that may relate to the variability in results reported in the original FAPAS series.
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Following the review a programme of experimental work was conducted to test hypotheses for poor results arising from the response to the survey.
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A report was prepared presenting the conclusions of the research and making recommendations for achieving good analytical performance for chloride.
The determination of chloride in food is, in theory, relatively easy, with the existence of several methods for extracting chloride from food as well as for analysis of chloride in solution. The overall performance of laboratories in the FAPAS series requiring the determination of salt or chloride has historically been poor, with an unacceptable proportion of laboratories failing to achieve an acceptable z-score.
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Having identified a particularly low proportion of laboratories achieving satisfactory performance in Series I Round 17, FAPAS sought additional information regarding methodology. However, its conclusions were not robust as the FAPAS Advisory Committee considered that the sample that had been circulated to laboratories for methodology testing, a fish paste with no added salt, was inappropriate.
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The proportion of laboratories achieving satisfactory performance in Series X round 16 was also particularly low, with some visual indication of possible bimodality to the data. Investigation by FAPAS confirmed bimodality. Since the FAPAS report presented limited information as to the extraction and quantification methods employed, no conclusive reason has been identified for this problem.
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A number of possibilities exist for poor performance in the determination of chloride content, including heterogeneous samples; difficulties in extracting the chloride from the sample; difficulties with the actual determination of the chloride and difficulties with expression of results.
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This project set out to investigate FAPAS performance and analytical methodology to try to identify the probable cause or causes of poor performance and to give guidance as to how performance can be improved.
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<p>Find more about this project and other FSA food safety-related projects at the <a href="http://www.food.gov.uk/science/research/" target="_blank">Food
Standards Agency Research webpage</a>.